The present disclosure relates to a semiconductor structure, and particularly to contact metallurgy for self-aligned high electron mobility transistors (HEMT's) and methods of manufacturing the same.
Most metallization schemes for high electron mobility transistors require a high annealing temperature above 900° C. to form low resistance Ohmic contact to a compound semiconductor material such as AlGaN. However, the integrity of a gate electrode for a high electron mobility transistor is compromised above 600° C. due to the reaction with aluminum in an Ohmic metallization scheme. Thus, use of such a high temperature anneal prohibits formation of truly self-aligned high electron mobility transistors in which a source region and a drain region are self-aligned to a gate electrode. Further, most of high electron mobility transistors are formed as normally-on devices, and it is difficult to provide a high electron mobility transistor that is normally turned off, i.e., turned off when no electrical bias is applied to the gate electrode.